Low boost problems

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graul

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Hi guys, i'm new here. I live in sweden and have an s3 2000 engine swapped from apy to a bam engine. It's equipped with a couple of fun parts, among them a gt28rs, fmic and a few other details.
The problem is that the previous owner of the engine had it mapped to about 300bhp at aprox 1.3bar (~18psi) and now it only boosts about 0.45bar (~6.5psi). I have done a smoke test and pressure test up to 1.5bar and i didn't find any leaks.
The n75 works as supposed and the dv too. I dont have any fault codes.
Does anyone have the slightest idea of where i should continue searching?

Thanks in advance!
 
sounds like its in limp mode but you should have codes?? turbo aint knackered is it? have you got vcds? tuffty or someone will chime in and tell you which blocks too log if so, you can then see what boost is being requested? also with a gt28rs it should be making alot more than 300bhp no? i would think 370+bhp more like it?
 
Yeah i think it's in limp mode too. I actually work at an audi/vw workshop (not as a mechanic) so i have access to vagcom, or audis VAS.
The turbo is ok no cracks or anything. I had a small leak between the turbo and manifold a couple of weeks ago but all i had to do was replace the gasket.
A little sidetrack, but hiw much power will an unopened bam engine hold? The guy who helped me with my ecu said it's mapped for about 300bhp.The gt28rs can deliver a lot more but the valves won't withstand it.
 
The valves will be fine, the rods are the weak point most agreeing 280bhp and similar torque being the edge of safety...guess you took everything over inc ecu obviously? I think boost is block 015 or 020... if it were in safe mode the ecu would throw a code. Check all your earths under the battery tray and clean mate.
 
I'll check block 015 and 020 tomorrow. Is that value from the map sensor g31 or somewhere else?
 
One of them is requested boost by the ecu, standard boost 12psi should be around 1800mps or something, it will be the figure in that ballpark anyway... mapped about 2200, and if your in limp around 900. Also try unplugging the maf and see if theres any change...
 
I was just out with a laptop hooked up and checked block 115. Requested boost is about 2550mbar and actual boost is about 1430. What do i do next? I feel lost and have absolutely no idea of where to look.
 
that means your arnt getting the boost the ecu is requesting... this means the ecu is happy, and your issue is likely mechanical, i.e something the ecu isnt aware off. check the actuator is holding pressure via a tyre valve and some silicone hose, pump it to 1.5 bar and see if it holds. pull the tip off and check for in and out play on the turbo shaft and check for any visible damage to the turbine. if its easy to remove the downpipe (guessing its ontop with your turbo so easy access?) have a look at the wastgate see if there is any damage, my mates evo 4 had a failed wastgate penny and it wouldnt boost at all. check for leaks around the turbo gasket and manifold. check the cat if it has one, has it broken up and clogged the airflow?

im definitely no an expert mate but ive had a few issues with my own turbo and thats what i would be checking.. had to take mine off and send it to bill for some work then fitted it along with the downpipe and v3 mani! was a nightmare. check all the pipework around the n75 closely too, check the n75 itself... even worth trying another n75 if you know anyone.
 
The thing is that i already put pressure in all the hoses and pipes to find leaks. The actuator is working and holding up to 1.5bar vacuum. There's no cat on it and the exhaust is leak free.
I'm thinking about buying a dawes device (?) and force it to run more boost. Tired of being run out by my dad's mk5 gti.
 
I tried a different n75 now with the same result.
But if i plug the vacuum line from the wastegate it works. Brobably won't cut it when needed to but that means the turbo works as supposed!
 
Maybe a weak or snapped wastgate spring then... anyone else got an opinion? The wastegate arm should be difficult to move?
 
checked faultcodes?
also log 118 to confirm what n75 is being told to do 95% being as "on" as it can = lots of boost

sounds like its stuck in limp mode or n75 is not working
 
audi upgrades
I'm reviving this thread from the dead as i still struggle with the car. Been running an mbc between the wastgate and n75. It works for a while if i clear codes but then the cel comes on and it starts to jerk real bad above 4000rpm.
I tried a LOT of things but now i just drive it with a cel and boost at 6.5psi.
I'm finally getting a code but it's the dreadful p1127, system running too rich.

I'm ready to drive it off a cliff or something. I really hope you guys can help me.
 
Have you made sure the DV isn't leaking boost? Did you try running it with the maf unplugged?
 
Yeah the dv is fine. I tried unplugging the maf but i'm just getting a fault code on it if i do that.
 
Out of curiosity what dv are you running? If it's not oem id just try running an oem one as it seems like you've tried everything else. But you wouldn't expect it to be causing this magnitude of a problem.

This is really well above my head, but it does sound like the turbo just can't make the boost.. :/
 
It's the stock one, 06A145710N if it matters. Also vacuum tested it according to the workshop manual and it holds vacuum as it should. I've tried another one too with the same p/n without any difference.
The turbo CAN make the boost, as i said i tried plugging the hose from the wastegate and it spools real good up to about 1.5bar, after that i let off the throttle.
 
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